1. Field of the Invention
This invention relates to a method of detecting knocking in an internal combustion engine and an apparatus therefor.
2. Description of Related Art
There are various kinds of known knock detecting methods and apparatus therefor adapted to detect a knocking phenomenon occurring in an internal combustion engine. For example, Japanese Patent Laid-open No. 45520/1983 discloses a knock detecting apparatus adapted to filter a frequency, which is peculiar to knocking, of an output signal from a knock detecting sensor, and to decide the occurrence of knocking by judging whether the amplitude of the frequency component exceeds a predetermined level or not.
However, in this prior art apparatus, a knock signal is always evaluated in the same range of crank angles, that is a predetermined "window" position and arcuate length of crank angles is used for the knock detection. Because the range over which knock detection is made is predeterminedly fixed, it is not possible to accurately determine the crank angle at which the maximum amplitude of knocking occurs. In this respect, the maximum amplitude of knocking varies with frequency and the present inventors have found that the frequency varies with crank angle position. If, as in the prior art, an overly wide window is used to detect the frequency of knocking, the window position also being fixed, so it has been found that noise frequency components based, for example, caused by the vibration of a valve, can have a major effect in the measurement window and cause a misjudgment of the frequency (and thus crank angle) of knocking.
It will be appreciated that the engine block has a particular resonance frequency and that the frequency of knocking in the prior art is detected by evaluating the energy of the vibration. As mentioned above, vibration from mechanical sources made by the operation of, for example, inlet and exhaust valves, cause other resonant frequencies. It is disclosed in Japanese Patent Application Laid-Open No. 63-219874 to use more than one filter to separate particular resonance frequencies. More than one filter is normally used if analog comprised of discrete parts are used or if digital filters are used.
However, both the above-mentioned prior art attempts to accurately detect the frequency and, hence, crank angle position of knocking are inflexible, and because filters are used it is essential that the central frequencies of the filters are predeterminedly fixed. This makes it impossible to correctly adjust the filters central frequencies to resonance frequencies in a situation where resonant frequencies change due to a change in the operating conditions of the engine and the aged deterioration of the engine itself. Thus, the prior art is unable to implement a high precision detection of knock in internal combustion engines. Moreover, the prior art attempt has the disadvantage that if analog filters are used, a like number of filters are required as the number of frequencies to be separated, thereby increasing the cost and size of the filters.
It is an object of the present invention to attain an improvement in knock detecting accuracy, which cannot be completely effected by the above known techniques, on the basis of the discoveries made by the inventors of the present invention in their various experiments concerning the relationship between the frequency of a detected knocking signal and a crank angle, and to provide a knock detecting method and apparatus, which are capable of improving an internal combustion engine output power and fuel consumption.